Respirators of the type to which the invention most nearly relates are those which utilize a half mask covering the mouth and nasal passage area, although various aspects of the invention relate as well to the so-called full-face mask respirators which not only cover the nose and mouth but provide protection for the face and eyes as well. Both the half mask and full-face respirators are provided with inhalation valves over which is mounted a replaceable filter or adsorptive cartridge so that contaminant-free air is drawn through the valves. The filter may be a mechanical filter element comprised of a fibrous filter material which provides protection against particulate matter such as dusts, mists or metal fumes, or a chemical filter media having a high adsorption capability, providing protection from gases and vapors. Generally, granular-activated carbon is utilized as the chemical adsorption media. Chemical and mechanical filters may be used independently or in combination in a single filter housing. Face masks respirators quite commonly utilize the so-called dual chemical cartridges with the cartridges mounted over inhalation valves located on each side of the face piece with a centrally-located valve in the mask being provided for exhalation. An alternative arrangement, preferred by some because peripheral vision is less restricted, provides a single cartridge and inhalation valve centrally mounted on the face piece with an exhalation valve mounted to one side. The present invention is adapted to be utilized in either configuration.
Known prior art includes: U.S. Pat. No. 2,640,481 to T. A. Conley, issued June 2, 1953; U.S. Pat. No. 3,744,524 to W. Z. Whipple, issued May 8, 1956; U.S. Pat. No. 4,179,274 to Moon, issued Dec. 18, 1979; U.S. Pat. No. 4,414,973 to Matheson et al, issued Nov. 15, 1983; U.S. Pat. No. 4,501,272 to Shigematsu et al, issued Feb. 26, 1985; and U.S. Pat. No. 4,592,350 to Maryyanek et al, issued June 3, 1986.